energy changes

• When chemical reactions occur, energy is conserved.
• An endothermic reaction is one that takes in energy from the surroundings so the temperature of the surroundings decreases.
• An exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases
• Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
• Activation energy = minimum amount of energy that particles must have to react
• label this

  A) exothermic

  B) reactants

  C) products

  D) energy change

  
• label this

  A) endothermic

  B) energy

  C) energy change

  D) activation energy

  
• exothermic: heat released to the surroundings, so products have less energy than reactants
• endothermic: heat taken in from surroundings, so products have more energy than reactants
• During a chemical reaction:

  o Energy must be SUPPLIED to BREAK bonds in the reactants

  o Energy is RELEASED when bonds in the products are FORMED